The proposed project is aimed at extending our observations that some tumors as well as normal endocrine tissue may be conditioned in vitro or in vivo to grow in untreated allogeneic recipients. The nature of the phenotypic (reversible) modulation in immunogenicity will be explored by looking at the characteristics of solubilized cell surface membrane antigens prepared from non-modified and modified tumors. Since the allogeneic host contributes to the graft survival or rejection, cellular and humoral responses will be examined in vitro by cytotoxicity and blocking tests and in vivo by cell transfer. Methods of combining allograft modification with minimal host immunosuppression to give optimal survival will be explored. BIBLIOGRAPHIC REFERENCES: Parks, R.C. and Jacobs, B.B. Transplantation behavior of allotransplantable tumor lines derived from immunologically modified hosts. J. Natl. Cancer Inst. 54: 1079-1083, 1975. Jacobs, B.B. and Kaliss, N. Induction of peritoneal ascites fluid by Freund's adjuvant: genetic and hormonal influences. Proc. Soc. Exp. Biol. and Med. 149: 146-150, 1975.